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Topic: IQ Cyo DC experiences (Read 8120 times)

I mentioned on the audax board that I was getting an IQ Cyo to play with, given that two lights are needed on PBP and my old Ay-Ups are getting shonky. Thought it would be worth documenting here since there's a wider audience.

On the understanding that you can run them DC from a standard battery, I soldered the dynamo tabs to a stock DC plug and in around 5 minutes time had the Cyo (plus wired tail-light) running happily from my Ay-Up battery.

However, when I actually had call to use them in anger (on Sunday's Nippy Sweetie), I was disappointed to find that the Cyo really doesn't put out very much light at all, even in the bright central "shaped" section of the beam. It was fine for pootling but I felt uncomfortable going fast, to the point where I just drafted someone with a brighter light when we got up towards 30mph.

By comparison, my 3 year old Ay-Ups are good for 40mph descents, as I've demonstrated to myself on several brevets as well as an unlit commute with many downhill sections.

Of course, the question is low consumption or inefficiency? In other words, does running the IQ Cyo on DC power simply draw a fraction of the current or is the DC to DC (!?) conversion burning ampage for nothing?

Tonight I broke out the multimeter to find:

Ay-Ups full beam - 290mA IQ Cyo - 190mAB&M Toplight Line Plus - 20mA

This is something of a relief - it means the Cyo is dim because it draws little current, which is not the worst thing in the world. Rigging up my remaining Ay-Up as a high-beam for descents would give me much prolonged battery life (50% more).

However, I'm curious as to why the Cyo draws so little current. I understand that it will accept 500mA from a dynamo hub - it would be nice to wire the one light with a high/low mode if possible.

Does anyone have any comment on the internal wiring of the Cyo that might shed some light on this? Should I dismantle it and wire the DC input directly (bypassing whatever the rectifying system might be)?

My electrician-foo is weak. I know only what I learned in standard grade physics.

What voltage are you putting across the Cyo?I've just taken a multimeter to mine, which is fed off 5.9V DC thanks to a nifty little DC-to-DC converter.

My Cyo has the standlichghththtght function, so ignoring the spike in current when it first gets turned on (charging the capacitor), it settles down to about 130mA, and it's adequately bright. (Especially as the brakes are siezed on, so the bike won't actually be going anywhere.)

My manual says 7.5V max and it's running from 7.4V (measured) at a current draw of 190mA. So 1.4W - half what it should take from an AC source.

I've tried powering it through the taillight connectors as apparently this circumvents some losses (in the sensor, rectifier, etc) but it doesn't seem noticeably brighter and still draws... 190mA.

It's very strange. I wouldn't say I'm unhappy because having a light that runs forever is also worthwhile, but it's vexing to not understand why. As I said, I'd be quite happy to ride with it at normal speeds (especially on dry roads) but I found myself dragging the brakes descending a straight hill which I basically knew was debris free - not ideal.

I'm not sure how far it answers your question, but I found the discussion on bikecurrent interesting - the thread that matters is titled 'B&M IQ CYO Internals'.

I don't pretend to understand all the discussion - I am not an electrical engineer, whereas these guys are practitioners with enquiring minds.

Still, I get the feeling that Pawel Danielewicz has been running a CYO on more than 8.5v DC, driven from the connectors that bypass the polarity-dependent circuitry that works with the usual dynamo input wiring.

You might want to think about posting your question on the bikecurrent list. I don't think there's an explicit answer there already.

Thanks for the link - that's quite a good discussion (although you're right, it doesn't really help me! Maybe it's implicit to all of them...)

At the end of the day I could dismantle the light and simply replace the internals with a voltage regulator (so it works just like my Ay-Ups only with a good quality reflector). But, part of the attraction of getting a dynamo light to run DC was that ultimately, I'd quite like a dynamo.

The new Philips LED light runs from batteries, of course, but it is almost 3x the price I paid for the Cyo, so not as attractive for experimentation - especially as I understand it has some sort of complicated button operation. On my recumbent, lights are down by my feet and anything which requires me to dismount to flick on "high beam" is a nonstarter.

Maybe they're being cautious about a recommended dc power because of cooling issues?

i.e. if it were running with a dynamo then you could expect plenty of airflow when there is higher power available. But a battery can (and will) keep applying full power when stationary, leading to higher internal temperature and reduced lifetime.

It's either that or they're assuming a current-limited source. The thermal issue does seem a bit more likely, given that it seems that the Cyo isn't close to the dynamo's current limit in normal operation. It's a bit expensive to do the experimentation to find out, though.

I'm not familiar with Ay-Ups, but could the Cyo be operating normally, and just outclassed by FRIKKIN' LASERS? I certainly prefer a bit more light than just a Cyo if I'm doing 30mph or more, especially if it's on a bike that's unforgiving of dodgy surface features.

You describe the Ay-Ups as good for 40mph descents. I've done a couple of 40mph descents with the combination of a Cyo, Ixon IQ on full whack and a head torch, which I'd describe as barely adequate. And that's on the Streetmachine, which is about as immune to unexpected surface hazards as bikes get.

The Cyo's a great light, but any dynamo light's going to be easily outclassed by something designed to get only a few hours run time for a reasonably sized battery pack...

I'll also add that rower40's Cyo appears to be about as bright as either of mine running from dynamo power at a normal riding pace.

I don't know the Cyo directly but I assume it uses the latest Cree XPG R5 emitter at about 3W. Whether your battery can give it 3W at the voltage it needs (about 3.5 - 4V as I understand the datasheet) depends on the battery and the voltage regulation. Since the Cyo is designed to run from a dynamo, I would not like to speculate what its electronics ends up doing with a DC source of about 7V. If it can make sense of the 7V DC it still has to be able to get the right current from the battery. 190mA is no where near enough by the sound of it; if it used the battery voltage without any losses (not likely but I don't know what the actual losses might be) you would need about 500mA from the battery to get anything like the full power from the light. Silly question, but I suppose the beam was in its 'high' mode.

EDIT: it can't be the battery's fault, of course, since it powers your au-ups which will be less efficient (light output per Watt) than the Cyo.

Chasing the links above, you would ideally want a current limited source. The IV curve is basically a rectified diode, and the voltage/current when connected with a dynamo thus behaves as you'd expect from that. See the message below

To be slightly more helpful, Pawel's graphs show a peak current of ~600mA on the dynamo, averaging more like 350mA. He doesn't specify speed for the test, but he's going past dynamo poles at about 160Hz if anybody familiar with typical dynamos would care to convert that.

Looking at the waveforms, I am certain that the output from the dynamo is being rectified onto a capacitor in the lamp. This explains why there is no current flow below about 4V (No current will flow until the dynamo voltage is higher than the voltage on the capacitor.

If you invert each half voltage cycle, then what you get is aprox the voltage waveform on the capacitor - which peaks at about 7V with about 1V ripple. (Disallowing for any diode drops - I assume they are using shottkey diodes or similar to minimise losses)

So if you are really putting in 7.4V, then you should be seeing full brightness. However, what is not explained is why you are only measuring 190mA (1.4W). What are you measuring the current with?

You don't need a current limited source - there must be internal current regulation in the light, or the LED would only last milliseconds.

I just find it a bit hard to visualise. If I cut the wires and touched them alternately very very fast (creating a crude AC source, like a dynamo) the light would suddenly draw over 500mA?

Instantaneously, immediately after you make the connection, as the current rushes in to top-up the internal capacitor. The current averaged over the whole cycle will be lower. If you took zero time to change polarity (ie. feeding it a true square wave), I wouldn't expect the capacitor to have time to discharge, so the current ought to be more or less the same as with DC.

It does seem increasingly likely that they're being conservative about the DC rating for thermal reasons (possibly in the rectifier? DC would mean that all the heat's being produced in two diodes rather than four...).

I don't think so. If you look at the waveforms linked to by Tom, the voltage waveform from the dynamo is close to an AC square wave (round topped) with a peak voltage of 7V. When this is rectified, it'll be pretty damn close to 7V DC - but in that instance is running at about 2.1W.

Looking at the waveforms, I am certain that the output from the dynamo is being rectified onto a capacitor in the lamp. This explains why there is no current flow below about 4V (No current will flow until the dynamo voltage is higher than the voltage on the capacitor.

Yes, definitely a rectifier in there, and a capacitor on the other side of it. The bigger question is what does the load beyond those look like?

And I'm suggesting that the answer is a diode, in terms of its current-voltage response. This basically means that it consumes very little current until you approach a threshold voltage, then quickly consumes a lot as you try to rise beyond that. Partly because that's what you'd expect from an LED and partly because it would explain the currents seen.

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So if you are really putting in 7.4V, then you should be seeing full brightness. However, what is not explained is why you are only measuring 190mA (1.4W). What are you measuring the current with?

Well, if my hypothesis is correct then the current consumption is highly sensitive to voltage in this region. So if you were to apply 7.5 or 7.6V then the current would be significantly higher than 190mA.

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You don't need a current limited source - there must be internal current regulation in the light, or the LED would only last milliseconds.

What I meant was a source which was actively controlled to limit current, not apply a fixed voltage. i.e what I should have called a current source. The point here is that because the load is very sensitive to voltage, if you were to try and apply any given voltage source then you may end up with significantly different currents. The variation largely is due to manufacturing tolerances, and temperature change. So you ideally want a circuit that varies the applied voltage in order to achieve a given current supply accurately.

They are suggesting a conservative voltage limit because they're afraid someone might not understand the above, and want to keep them on the safe side of the actual limit. What isn't clear is what the real current/power limit is. My guess is it's thermal, and they don't want to say what because it depends on airflow and they want to clearly make sure they've recommended something is safe when homebrew nutters come back and blame them after they fry their LEDs.

There is a bit more information about the upper limit protection, and about applying dc, if you read down the quoted messages in the post I linked before.

It's a lipo battery with some circuitry, but clearly it's not current limited as it will happily supply two pairs of Ay-Ups at almost 300mA each = four times the current drawn by the Cyo.

It's not a case of a magic current limit for the battery - the battery has an effective internal impedance and voltage and this in combination with the load determines current. The highest current it can supply is when it's shorted and is only outputting at 0V. At open circuit with no current it will give largest voltage. As soon as you draw some current it goes down, but the result is highly dependent on the load I-V curve.

Assuming you don't have a bench power supply to check dc current against voltage, can you redo your test with a fully charged and a very low battery? And at the risk of being insulting, can I check you're measuring the battery voltage when loaded in both cases, not open circuit? Similarly for your 7.4V answer - was that open circuit or at 190mA?

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I just find it a bit hard to visualise. If I cut the wires and touched them alternately very very fast (creating a crude AC source, like a dynamo) the light would suddenly draw over 500mA?

I don't think you are right there Tom. The load beyond the capacitor will be a current regulator followed by the diode.

Power leds (certainly the one in the CYO) have a typical forward voltage of about 3 to 4V. If you apply 7V from the capacitor (which has been charged by the rectified AC waveform) then the led will pop very very quickly.

Therefore there must be a current regulator between the capacitor and the diode. Now it would seem that this regulator is pretty far from a perfect current source - since the input current increases with increasing voltage. It could be as crude as a resistor - although this would be very wasteful of power, so I don't think that will be the case.

The volt/current chart on that page suggests that they have not implemented a proper current control (although it must be providing some current limit function). If they were, I would expect the current to go up with volts until the regulator were able to deliver the controlled current - then I would expect the input current to drop as the voltage increased further (constant power into the led). From the graph at this link, it appears not to be the case.

Tom may be right that the way to get full power out of the light with an external battery is to provide an external current source, rather than voltage source.

I don't think you are right there Tom. The load beyond the capacitor will be a current regulator followed by the diode.

Yes, I was talking more of its behaviour than what was actually there. Certainly I was expecting some kind of switched mode to change the voltage, but that doesn't rule out the diode load characteristic.

That curve you found for the Fly is very revealing. The difference to the 'warm' curve doesn't bode well for a simple battery supply, alas..

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It could be as crude as a resistor - although this would be very wasteful of power, so I don't think that will be the case.

The volt/current chart on that page suggests that they have not implemented a proper current control (although it must be providing some current limit function). If they were, I would expect the current to go up with volts until the regulator were able to deliver the controlled current - then I would expect the input current to drop as the voltage increased further (constant power into the led). From the graph at this link, it appears not to be the case.

Actually makes a little sense for a dynamo driven light, if you're expecting the limit to be thermal...

Just to confirm - I measured the voltage under load. That is, I ran the Ay-Ups (measured the current at 290mA) and then measured the voltage across the rejoined wires with the light still on, which was 7.49V.

It's interesting that there is no thermal grease between the diode and the heatsink in the dismantled Fly - it would seem to me that this is pretty fundamental.

It sounds increasingly like if you want more light from the Cyo, it's a straight swap on the existing circuitry with some kind of dimmable driver. As it is, I'm going to take it out on another wet night somewhere and make a call on whether I'm happy with it driven at 190mA (which would be nice, no dismantling needed).

For descents, I can just switch in the Ay-Up (and in any case, I need two lights on the bike for PBP).

Fair enough. I'd still check the current with a fully charged and nearly flat battery.

If you're going to open it up and start substituting the circuitry anyway, it might be worth exploring exactly what the circuit is first to see if you could achieve what you want more easily with a couple of component changes?